Micromechanical oscillating device

ABSTRACT

A vibrating microdevice, such as a vibrating micromirror, includes a vibrating structure which is connected to a supporting body via at least one spring structure in an at least a largely floating manner, the spring structure including at least one torsion-spring element defining a torsion axis and permitting a torsional vibration about the torsion axis to be induced in the vibrating structure, the spring structure also including at least one converter structure, which at least partially converts forces acting at least largely perpendicularly to the torsion axis on the torsion spring element into forces acting at least partially parallelly to the torsion axis on the torsion-spring element.

FIELD OF THE INVENTION

The present invention relates to a vibrating microdevice, such as avibrating micromirror.

BACKGROUND INFORMATION

Vibrating micromirrors, which are manufactured using surfacemicromechanics and have a variety of forms of springs and suspensions,are conventional. For example, German Published Patent Application No.198 57 946 describes micro vibrating mirrors, which are used in sensingthe passenger compartment of motor vehicles, in scanning, or for laserdeflection.

Conventional vibrating micromirrors (e.g., those manufactured fromsilicon with the aid of micro-mechanical methods) are only be operatedat relatively small operating or torsion angles. In order to attainoperation at large torsion angles, springs, from which the actual mirrorsurface is suspended from a supporting body in a largely floatingmanner, must be designed to be very thin, since only relatively smalldriving forces (e.g., forces for inducing a torsional vibration) areavailable.

However, in the case of the mirror surfaces being relatively large incomparison to the spring thickness, externally applied forces, which,e.g., occur in response to a bump or collision, occasionally result inthe destruction of the springs by breaking or tearing.

It is an object of the present invention to provide improved springs ofa vibrating microdevice, in particular a vibrating micromirror. In thiscontext, the springs may connect the actual vibrating surface to asupporting body in a largely floating manner, allow a torsionalvibration of the vibrating surface, and absorb and deflect forces (e.g.,external forces) that act suddenly and are directed at least partiallyperpendicularly to the vibrating surface, so that the springs areprevented from breaking.

SUMMARY

The vibrating microdevice according to the present invention includesspring structures that reduce the mechanical workload of the actualtorsion-spring elements, especially with regard to bending stresses.This arrangement allows the torsion-spring elements to be designedthinner, which permits the use of smaller forces to induce a torsionalvibration of the vibrating structure. In addition, a longer travel(i.e., greater torsion angle) may be achieved by these forces.Furthermore, the vibrating microdevice of the present invention reducesthe load on the torsion-spring elements during the manufacturingprocess, which results in fewer losses during production.

In addition, the thin torsion-spring elements, in connection with thesmaller applied forces for inducing the torsional vibration, may reducethe outlay for electronically controlling the vibrating microdevice. Atthe same time, the increased robustness of the vibrating microdeviceaccording to the present invention also allows manufacturing tolerancesto be reduced during the manufacturing process, so that simpler and morecost-effective manufacturing methods may be used.

In addition, the vibrating microdevice of the present invention remainsrobust in the case of mobile use, while simultaneously being constructedsimply and having less outlay for connection techniques, which leads tocost savings.

Further, production of the microdevice according to the presentinvention does not require new manufacturing methods. The device may beproduced completely by conventional technologies. Moreover, additionallyprovided converter structures may be produced in the same method step asthe production of the vibrating structure and the torsion-springelements.

The greatest mechanical load on the spring structure of the vibratingmicrodevice according to the present invention generally occurs inresponse to a sudden impact. In this context, the impact energy and theimpact momentum are mainly transmitted to the vibrating structure. Thevibrating microdevice and an employed converter structure of the presentinvention may absorb the energy stored in the movement of the vibratingstructure through elastic deformation of the spring structure.Particularly, the converter structure damps the transmitted momentum,which results in the torsion-spring elements being largely subjectedonly to tensile stresses, which are directed essentially parallel to thetorsion axis of the torsion-spring elements. These tensile stresses areuncritical and rarely lead to tears or breaks of the spring structures.Undesirable bending stresses, which frequently cause conventionaltorsion-spring elements to break, may be absorbed by the converterstructure, partially damped, and at least partially converted touncritical tensile or compressive stresses.

The vibrating microdevice of the present invention is capable ofabsorbing and tolerating markedly greater forces, including those ofshort duration, since the torsion of the converter structuresconsiderably lowers the bending stress of the torsion-spring elements,especially at the transition or connection points, the critical tensilestress for the torsion-spring elements being markedly greater than thecritical bending stress.

In addition, rectangular or angular transitions or structures of theconverter structures or the spring structures may be rounded, resultingin a further increase in rigidity. Furthermore, the configuration of afirst converter structure attached between the torsion-spring elementand the supporting body may differ from that of a second converterstructure attached between the torsion-spring element and the vibratingstructure. Differing configurations may also be employed if a pluralityof spring structures are used to connect the vibrating structure to thesupporting body. The spring structures may then have differentconfigurations as well. In this context, the term configuration includesshape of the structure, materials used, and/or material strength.

The vibrating microdevice of the present invention may also be providedwith stop structures, which limit, to maximum values, a local movementof the vibrating structure from a neutral position exceeding thetorsional vibration and directed parallel and/or perpendicular to thedirection of the torsion axis. Consequently, the upper limits orcritical maximum values of elongation or bending of the torsion-springelements or the converter structure may be preselected, in order toprevent additional breaks or tears.

Further, the stop structures may be flexible as well, so that they areable to cushion or damp a local movement of the vibrating structureexceeding the torsional vibration, from the neutral position, paralleland/or perpendicular to the direction of the torsion axis. This providesadditional protection from tearing or braking at critical loads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example embodiment of the present invention, inthe form of a vibrating micromirror.

FIG. 2 is a cross-sectional view of another example embodiment of thepresent invention, including a modified spring structure.

FIG. 3 is a cross-sectional view of a further example embodiment of thepresent invention, including a modified spring structure and a modifiedvibrating structure.

FIG. 4 is a cross-sectional view of yet another example embodiment ofthe present invention, including a modified spring structure.

FIG. 5 is a cross-sectional view of another example embodiment of thepresent invention, including an additional stop structure.

FIG. 6 is a cross-sectional view of another example embodiment of thepresent invention, including additional stop structures.

FIG. 7 is a cross-sectional view of one of the spring structures of theexample embodiment illustrated in FIG. 1.

FIG. 8 is a cross-sectional view of a modification of the springstructure illustrated in FIG. 7, including an additional stop structure.

DETAILED DESCRIPTION

FIG. 1 illustrates a vibrating microdevice 5 in the form of a vibratingmicromirror, including a vibrating structure 10 made of a rectangularflat plate. The plate is connected in a largely floating manner to asupporting body 14 surrounding vibrating structure 10 via twosubstantially identical spring structures 13 lying opposite each other.Each spring structure 13 includes a torsion-spring element 11, each ofwhose two ends are connected to a converter structure 12 having theshape of a handle. Converter structures 12 are directly connected tosupporting body 14 or directly connected to vibrating structure 10.

In an example embodiment according to the present invention,torsion-spring elements 11 are positioned with respect to each other sothat they are on a common axis that defines torsion axis 20, a torsionalvibration about the torsion axis 20 being inducible in vibratingstructure 10. Torsion axis 20 extends parallel to the x direction. Forexample, vibrating structure 10 has a width of 4000 μm, a length of 4000μm, and thickness of 50 μm. Torsion-spring elements 11 may be 5 μm to 15μm wide, 300 μm to 1000 μm long, and approximately 50 μm thick. In theexample embodiment illustrated in FIG. 7, the length of the torsionspring element is 600 μm, and its width is 10 μm.

Furthermore, converter structures 12 typically have a thickness of 50μm, with the width of the cross-pieces forming converter structures 12being 10 μm to 50 μm, and a length of 100 μm to 1000 μm. In the exampleembodiment illustrated in FIG. 7, the length of the converter structureis approximately 600 μm and the width of the cross-pieces isapproximately 15 μm.

In addition, the corner and transition regions, i.e., the regions inwhich converter structures 12 are connected to supporting body 14,vibrating structure 14, or torsion-spring element 11, may be rounded andwidened in order to attain an increase in rigidity.

Furthermore, vibrating microdevice 5 is made of silicon, a siliconcompound, or another micropatternable material, and produced usingmicro-mechanical patterning methods. Also provided for operatingvibrating microdevice 5 are arrangements, such as electrodes,piezoelectric actuators, or magnetic actuators, which are arranged belowvibrating structure 10 or extend on the surface of spring structures 13and/or on the surface of vibrating structure 10, and produce torsionalvibration of vibrating structure 10 about torsion axis 20, usingelectrostatically or mechanically induced forces. The torsion angle is,for example, ±10°. In addition, conventional electronic components maybe provided, such as connection contacts, printed circuit traces, andevaluation and control electronics.

During operation of vibrating microdevice 5, torsion-spring elements 11are torsionally loaded in the case of a torsional vibration abouttorsion axis 20, vibrating structure 10 rotating about torsion axis 20.If external forces occur, especially ones of short duration (e.g., thoseforces which result from a bump or crash and act on vibratingmicrodevice 5, e.g., in the positive or negative z direction, i.e., atleast partially perpendicular to torsion axis 20), converter structures12 may bend or twist, so that torsion-spring elements 11 are onlysubjected to a markedly reduced bending stress in the z direction. Thebending of converter structures 12 produces uncritical tensile stress intorsion-spring elements 11.

In response to an overload of short duration or a peak load, converterstructures 12 may allow a bending stress acting on torsion-springelements 11 to be converted into a stress, which is aligned in adirection that is at least substantially parallel to torsion axis 20.This prevents torsion-spring elements 11 from breaking or tearing.

In response to torsion and bending caused by an external force in the zdirection, converter structures 12 are essentially subjected to atensile load, as well.

But, if converter structures 12 are omitted so that torsion elements 11are each directly connected to vibrating structure 10 or supporting body14, then a maximum bending stress, which cannot be compensated for,occurs at the ends of torsion elements 11, in response to the externalforce acting in the z-direction. This may often lead to breaks at thesepositions in response to supercritical forces.

The example embodiment illustrated in FIG. 1, may convert undesirableand critical bending stresses, which are pointed in a direction at leastpartially perpendicular to the direction of a torsion axis, intotolerable tensile or compressive stresses that are at least essentiallyparallel to a torsion axis 20.

In this context, converter structure 12 may be configured so thattorsion elements 11 essentially do not experience tensile loads, butrather experience only compressive loads.

In the embodiment illustrated in FIG. 1, it is not essential to providetwo torsion-spring elements 11 or spring structures 13 arranged oppositeone another. Instead, one spring element 13 may be provided, whichconnects the vibrating structure 10 to supporting body 14 in a floatingmanner and supports the vibrating structure. The direction or geometryof torsion spring element 11 defines torsion axis 20. Furthermore, fourspring structures may be provided, which are offset 90° with respect toeach other and form diametrically opposed pairs. In this manner, twoperpendicular torsion axes 20 are formed, and, in response to torsionalvibrations controlled independently of each other being induced aboutthese torsion axes 20, vibrating structure 10 traces path linescorresponding to a Lissajou figure.

FIG. 2 is a cross-sectional view of a second example embodiment of thepresent invention. FIG. 2 illustrates a spring structure 13, which ismodified in comparison with the spring structure illustrated in FIG. 1.In particular, each spring structure 13 illustrated in FIG. 2 includesonly one converter structure 12. The converter structure may be directlyconnected to vibrating structure 10 on one side and directly connectedto torsion-spring element 11 on the other side, the torsion-springelement being directly connected to supporting body 14. However, it ispossible to interchange the roles of vibrating structure 10 andsupporting body 14.

FIG. 3 is a cross-sectional view of a third example embodiment of thepresent invention. In this example embodiment, a recess is provided invibrating structure 10, into which converter structure 12 is inserted.In comparison with the example embodiment illustrated in FIG. 2, thisconstruction saves space needed for converter structure 12 and booststhe wafer yield. In addition, this arrangement allows torsion-springelement 11 to be lengthened in a space-saving manner. Furthermore, theroles of vibrating structure 10 and supporting body 14 may beinterchanged (i.e., converter structure 12 may be inserted into a recessin supporting body 14).

FIG. 4 is a cross-sectional view of a fourth example embodiment of thepresent invention. In this example embodiment, a closed hollow contourincluding a rectangular periphery is provided as a converter structure12. This hollow contour does not increase the permissible externalforces, and therefore the load capacity of vibrating microdevice 5 assharply as the example embodiments illustrated in FIGS. 1 to 3. But, itmay allow coupling of driving forces via converter structure 12, inorder to induce the torsional vibration in vibrating structure 10.

FIG. 5 illustrates a modification of the example embodiment illustratedin FIG. 2. In this example embodiment, a stop structure 15, which may bemade of the same material as spring structure 13, is provided. The stopstructure 15 is directly connected to vibrating structure 10 in twoplaces, while torsion-spring element 11 is directly connected tosupporting body 14. Stop structure 15 may be configured to be flexible.However, it is configured as a rigid stop structure 15 as illustrated inFIG. 5. In addition, the roles of supporting body 14 and vibratingstructure 10 may be interchanged.

Stop structure 15 causes a local movement of vibrating structure 10,which is from the neutral position, is parallel (x direction) andperpendicular (y direction) to the direction of torsion axis 20, is, forexample, caused by impact, and exceeds the desired torsional vibration,to be limited to subcritical values.

Thus, in addition to the function of converter structure 12, the dangerof breaking or overloading is prevented. The flexible or rigid design ofstop structure 15, which is preferably somewhat thicker than springstructure 13, also prevents torsion-spring elements 11 from beingoverloaded, without impairing their functionality.

In response to a force in the z direction, which places a tensile loadon torsion-spring element 11 and a bending load on converter structure12, stop structure 15 limits the deflection of converter structure 12and, therefore, removes load from converter structure 12. Therefore, theresult is an overall load which, apart from the tensile load oftorsion-spring element 11, essentially only affects stop structure 15.

FIG. 6 illustrates a modification of the example embodiment illustratedin FIG. 1. FIG. 6 illustrates an example embodiment for completelyprotecting a spring structure 13, using appropriately placed stopstructure 15.

An additional increase in rigidity may be attained by rounding offrectangular or angular transitions or structures of converter structures12 and/or of stop structures 15.

Depending on the utilized technology and strength requirements, e.g.,with regard to the shape, spring structures 13 may be connected tosupporting body 15 in a different manner than that connecting springstructures 13 to vibrating structure 10.

FIG. 7 illustrates one of the spring structures of the exampleembodiment illustrated in FIG. 1 to scale.

FIG. 8 illustrates a spring structure 13 including a stop structure 15,which is connected to vibrating structure 10 in a rigid manner.

What is claimed is:
 1. A vibrating microdevice, comprising: a supportingbody; at least one spring structure having at least one torsion-springelement and at least one converter structure, the torsion-spring elementdefining a torsion axis; and a vibrating structure connected to at leastthe supporting body by the spring structure in a largely floatingmanner, a torsional vibration of the vibrating structure inducible aboutthe torsion axis; wherein the converter structure at least partiallyconverts external forces acting at least substantially perpendicularlyto the torsion axis into forces acting on the torsion-spring element ina direction parallel to the torsion axis.
 2. The vibrating microdeviceaccording to claim 1, wherein the at least one converter structure isconfigured to at least partially convert the external forces intotensile forces acting on the torsion-spring element.
 3. The vibratingmicrodevice according to claim 1, wherein the spring structure, thevibrating structure, and the supporting body are each made of one ofsilicon and a silicon compound.
 4. The vibrating microdevice accordingto claim 1, wherein the converter structure is directly connected to atleast one torsion-spring element.
 5. The vibrating microdevice accordingto claim 1, wherein the converter structure is directly connected to oneof the vibrating structure and the supporting body on one side anddirectly connected to the torsion-spring element on the other side. 6.The vibrating microdevice according to claim 1, wherein the converterstructure is only directly connected to the torsion-spring element. 7.The vibrating microdevice according to claim 1, wherein the at least onespring structure includes one of a single spring structure, two springstructures arranged on one torsion axis and four spring structuresarranged on two perpendicular torsion axis.
 8. The vibrating microdeviceaccording to claim 1, wherein the vibrating structure is a largelyfloating and flexibly supported mass.
 9. The vibrating microdeviceaccording to claim 1, further comprising a vibrating device configuredto induce the torsional vibration of the vibrating structure.
 10. Thevibrating microdevice according to claim 1, wherein the converterstructure is one of bow-shaped, arched, handle-shaped, and semicircular.11. The vibrating microdevice according to claim 1, further comprisingat least one stop structure, the stop structure one of flexible andrigid, the stop structure configured to limit to a maximum value a localmovement of the vibrating structure from a neutral position, which isone of parallel and perpendicular to a direction of the torsion axis andexceeds the torsional vibration.
 12. The vibrating microdevice accordingto claim 11, wherein the stop structure is connected to one of thevibrating structure and the supporting body.
 13. The vibratingmicrodevice according to claim 1, wherein the vibrating structureincludes a planar plate.
 14. The vibrating microdevice according toclaim 13, wherein a shape of the planar plate is one of rectangular,square, circular, and elliptical.
 15. The vibrating microdeviceaccording to claim 1, wherein the vibrating structure is formed in theshape of a concave mirror.
 16. The vibrating microdevice according toclaim 1, wherein the converter structure includes a closed, hollowcontour.
 17. The vibrating microdevice according to claim 16, whereinthe closed, hollow contour includes one of a ring-shaped, elliptical,and rectangular periphery.
 18. The vibrating microdevice according toclaim 1, wherein the vibrating microdevice is configured as a vibratingmicromirror.